const int ledPins[] = {2, 4, 5, 18};  
const int upButtonPin = 12;         
const int downButtonPin = 13;         

int counter = 0;                     
int maxCounter = 15;                 
void setup() {
  
  for (int i = 0; i < 4; i++) {
    pinMode(ledPins[i], OUTPUT);
  }

  
  pinMode(upButtonPin, INPUT_PULLUP);
  pinMode(downButtonPin, INPUT_PULLUP);

  
  Serial.begin(115200);
}

void loop() {
  if (digitalRead(upButtonPin) == LOW) {
    
    counter = (counter + 1) % (maxCounter + 1);
 delay(200);  
  }

  if (digitalRead(downButtonPin) == LOW) {
    
    counter = (counter - 1 + maxCounter + 1) % (maxCounter + 1);
    delay(200);  
  }

  
  for (int i = 0; i < 4; i++) {
    digitalWrite(ledPins[i], (counter >> i) & 0x01);
  }
}